Ion trap gun



. l, 1953 D. D. VAN ORMER ION TRAP GUN 2 Sheets-Sheet 1 Filed NOV. 7, 1951 INVENTOR Dal/1a DVazz Ormer Dec. 1, 1953 D. D. VAN ORMER 2,661,436

ION TRAP GUN Filed Nov. 7, 1951 2 Sheets-Sheet 2 INVENTOR David Tkmflrmer 00000040 ATTORNEY Patented Dec. 1, 1953 ION TRAP GUN David Dale Van Ormer, Lancaster, Pa., assignor to Radio Corporation of America,

of Delaware a corporation Application November 7, 1951, Serial N 0. 255,186

10 Claims.

This invention is directed to cathode ray tubes and specifically to gun structures for such tubes incorporating structure for trapping negative ions in the cathode ray beam.

In cathode ray tubes utilizing a single electron gun, various expedients have been used for trapping negative ions in the electron beam. It is believed that such negative ions originate in or near the cathode surface of the electron gun, and are directed and accelerated with the electron beam toward the fluorescent screen of the cathode ray tube. Continual bombardment of the fluorescent screen by these heavy negative ion particles has resulted in a darkening of the screen near its center, which is attributed to a decomposition or "burning of the phosphor material constituing the fluorescent screen. To eliminate such screen burning, arrangements of electrode structure between the cathode electrode and the fluorescent screen'have been used to provide a trapping device or means to prevent the heavy negative ion particles from reaching the fluorescent screen of the tube.

This invention is directed to cathode ray tubes of the type having an electron gun structure for forming a plurality of electron beams which are focused and brought to convergence on the fluorescent screen of the tube by a magnetic lens .field. Such multiple beam gun structures may be used in cathode ray tubes in which the multiple beams are brought to a common point of convergence at the fluorescent screen by a magnetic focusing coil. Such applications find use in projection-type cathode ray tubes, in which an intensely brilliant picture is desired for projec- -:ti on upon a screen. Also such plural beam guns find use in color television reception, in which itis necessary to separately modulate each beam -Wi'bh a different color signal. Such an application is disclosed in the co-pending application of H. v(1,. Moodey, Serial No. 166,416, filed June 6, 1950. In suchapplications it is desirable that the heavy negative ion particles which constitute a portion of the electron beam be eliminated from the beam before it strikes the phosphor screen.

It is therefore a purpose of this invention to provide a negative ion trap structure for a plural beam electron gun;

It is a further object of this invention to provide a simple ion trap structure for a plurality of electron beams directed toward a fluorescent screen.

It is another'object of this invention to provide 2 the electron gun structure of a cathode ray tube.

It is a further object of the invention to provide a method of trapping negative ions in a plurality of electron beams with the use of the magnetic lens which focuses and converges the electron beams at the fluorescent screen.

The invention is to a-multiple beam cathode ray tube using an ion trap to prevent screen burning, during tube operation. The invention utilizes the magnetic focusing and converging coil together with gun electrode trapping structure for preventing the negative ions in each beam from striking the fluorescent screen. The gun electrode trapping structure comprises an opaque electrode barrier structure positioned in the path of each of the electron beams which blocks or traps the negative ions in each beam. A focusing coil is used for deflecting or directing the electrons of each beam away from the blocking barrier structure. Since the negative ions are little affected by the magnetic focusing field, they continue along the original beam path to strike the barrier Modifications disclose beam diverting electrodes for directing the electron beams toward theion trap barriers, in combination with the focusing field for directing the electrons of each beam away from the ion barrier electrodes.

Fig. 1 discloses a sectional view of a plural beam cathode raytube incorporating an ion trap in accordance with the invention.

Fig. 2 discloses a partial sectional view of an alternative form of plural beam cathode ray tube having an ion trap in'accordance with the invention.

Fig. 3 is a sectional view of the structure of Fig. 2 and along the sectional line 33.

Fig. 4 is an alternative form of a plural beam cathode. ray tube utilizing an ion trap structure.

Fig. 1 discloses a cathode ray tube It) having a tubular neck portion 12, within which is mounted an electron gun structure I4. The electron gun I4 is one, which provides a plurality of electron beams l6 directed into a bulb portion I8 of the tube envelope l0. Bulb portion I8 is closed by an end wall portion 20 having on the inner: surface thereof a film of phosphor material 22 forming a luminescent screen. Electron gun structure It includes a plurality of cathode electrodes 24 consisting of tubular members mounted parallel to each other and symmetrically disposed about the axis of the tubular neck portion l2. The

' to the phosphor screen 22, by solid wall portions grid 26 closed, at the end adjacent the phosphor screen 22, by a wall portion 28 having an indented portion extending parallel over the angularly dis posed surfaces of the cathodeqelectrodes-M.- wall portion 28 has apertures, [overlying the:

coated surface of the cathode electrodes, one over each cathode surface for the massage. thereaxis in the same manner as are the negative beam electrons. Due to their heavy mass, these negative ions will strike the fluorescent screen 22 with sufficient energies to damage or burn the screen. The effect of negative ion bombardment on the fluorescent screen is the formation, after a period of time, of a brown or burned area where ;theiions strike. To prevent theznegative ions in .the electron' beams from-passing to the fluorescent screen 22, the accelerating electrode 33 is provided with a limiting apertured barrier wall zPortion 31 which is positioned in the paths of the electron beams diverging from the common crossover nointfifi." When the electron beams are conthrough of electrons from the activated cathode surfaces. An accelerating electrode fil ies-post tioned along the axis of the envelope neck l2 and clos ely :sna d H m (control electrode :35- eoceleratin elect od :is cl sed :by :a centrally z e nre {wall po ion 82 .sh ine mor ionlsurim nding th tr l rep tureex en i giinto th indented portion of m son-n .1 rid Wallis, .es

sh w Qhe .zsn cifi e ectron un st ucture edelscribed, :is d closed in g eater detail in the ;pending -,applicationof D. ,?D. Nan :Qrmer, zserial :NQ. ;2 B.;' 5,' ;:,fi1 s :SQR m I-;26, 195l- F fhis linventien i not edi ectedsto the speci c un s... 110- tun i isslosedrin th psi-pe d ng application, i-but time un atru tum is "merely describeda ulm traitiv .Qf mendin a rplu a'lity of electron beams-c5.

5 1116 521313 :stnucture I'Awalso includes-a :sscond acce rating electrod 3.3 spaced a lmgr e tax s inf envelop 12' and-between the :Screen :2 and accelerating electrode in. fllhe portion Of the iinner surfacegofzthe :tuhe envelope til between acceleratin electrode 33- :and ethe zfiuoresoent scre n 32 is 2coated=with la cenduetive coating 534 :suchms :carbon, which :is lconductively connected :to accelerating electrode :33 by spring spacer finn rs :35. The electrons emittedabyecathodesfl l are :urged through :thelapertures of eoontrolwgr-id portion 2,8 iby the accelerating :field :of electrode :3D.- fllhe electrons massing through leach-control grid aperture form a beam which convergesito a first crossover point .on the :aXis .of lthe tube .neck portion 12. ilfhe .design :and arrangement of the gun structure=is such ithat the :crossover zu ints :of cach ielectron l eam awill moincide in a restrict d re ion 135! beyond which \the teams 1 l6 wi l -abuser i d er gram-ea h other and dram the common crossover point 38. im filngtfield prmlidfid. .by {a foc si g oi 40 having ametaleasinafl ipr r d ne t eefl x at tith neld f qoilflfl- Eocusiri Q JUS m un on J'Jce tube .neck 12. .so that the mou ing fiel formed is oaxial with the tube- .ffur h nznp the coi 4 is po it oned .s 'tha the fie d o .th coil will converge all electrons issuing from the common crossover point 138 to a common point on the fluorescent screen 22. i The focusing coil W, as described in grea' ter detail in the above .cited -co-pendin application of Van Ormer, also brings theelectronswithin each-beam into sharp focus at -:the --convergence -point on thescre'en. This is {schematically shown 'rby'ithexdotted 'beam :paths illustrated in File. 1.

'i lhere are .:fo.11me.d either :in'xthe cathQdewmittine urface or ad acent to t e rathodeeemittine su s lnesat iqn which may e o o y e eo qf t e ma erial. fie au .q lthe r negative :ha ;s.e thes ions a a c l ra ed down th ube A ma neti r -.vergedrby-the rfield of focusing coil 40, the barrier wall 31 -will efiectively block the negative ions as they, winotlafiected by the focusing field.

The voltages disclosed in Fig. l, as being applied to --the :several electrodes, are not limiting but illustrate the conditions under which a tube of :the :type .diiSGlQBfid-fil Mg. .1 may 'I'bfi successfully operated.- 110 adjust the ivolta es :so what-the lion :trap :is effective, xthe magnetic :focufiing ifield coil is first set at zero. if-hewroflmge QQfkflflQQl aerating electrode 3.0iisithenraiseduntilthebea leaving the gcommonaerossover point :38 are :snf- :fioiently divergent zthat ithey :are completelyrcu ioff'afrom rthe'zfiuorescentzscreen 22 by ithe zbarrier .sa-pentur-e :3-1; .I his; then assures rthat :the'iicns twithin theibeam will-ralso -tbe out 01f abyrtheiiun trap portions :The current :in :the'tiocusm coilis now :increasedxuntil'cthe :electron beam appear on the screen rand are ibrought rtugetber :t -;-the -:point .of common {convergence :and'rfomzs. :Si-nce athe :nega-tive 'Ii0ns of .iihedhEflU are no :affiected :by rt-he meld-m :focusing: coil .qfll'pthey are effectively blocked lby .theeopaque-iion :trazp barrier'm. ilfheelectrorvbeamsanasmnowibegscarmed overithekfluonescentiscreen 22 in :any well-:lmosvn mannergasiby magneticldefleoting fields-provided "by atwomairs .of edefiectingvcqils mounted, 'as is shown, ante-s oke @structure all. :Themonstruction of the scanning yoke 44 and its mode ofropor'aition for scanning rthe beam over :the'screen' suriface smay :beuconventionalrand "is lnot described i-n further-detail; I 1

I Figures 2 and 3 .discloseaan ialtennative of plural Pbeam electron -.gun istructure monsistring of a plurality-10f parallel electron .guns, each :having a tubularcathode 46', sa wontrol :grid 58 8, first accelerating electrodes 2'50, and :second nac- .-celerating electrodes 52. Electrodes 118350, and #52 :may tied .electrically'ito ztheir corresponding pa'rit in themtherelectron guns. whe eintron beams of the tube may be sepa-rately motl- :ulated' by applying -.independent signali voltagcs between each cathode nts'and its-respective won'- trol grid fl. Electrons from the cathodes flfi are formed; as is :schemeitlcally shown', into 0100- tron' beams' 53 vvhichpass through accelerating 55 t ed e ec rica l t a p n ust ve al c ati 5.8.; c rrespondin to coa ing 1 o .Eia- 1.- .Accelerating electrode 56 is maintained atlahi her ,nos ti mtent a tha e ectrode.

- ,flocus n e ctmde .55! ha -p .a ity f short tubular e e ents \60 al n d wi h each .of the electron guns and provides with the adjacent mention of accelerat ne el ctrodes 52 a .iocu i Qiield fo co tribu ing-42. aah beam-a wmelgging ea ner al i cusineefiect. A common focusing and beam converging field is established by a focusing coil 62. The field of coil 62, as disclosed in Fig. 1, brings the electron beams 53 to a common point of convergence and beam focus at the fluorescent screen of the tube. The third accelerating electrode 56 is formed with an apertured wall portion 64, out of alignment with the electron beam paths 53.

The potentials indicated in Fig. 2 are illustrative of those which may be applied for tube operation. The adjustment of the electrode potentials of the tube are made as follows. With the current of coil 62 set at zero, the potential of electrodes 54 and Er: are made equal. The

electron beams then issuing from focusing electrode 54 will pass down the tube and clear the electrode wall 64. The potential of the accelerating electrode 56 is then made more positive relative to the potential of focusing electrode 54 to cause the beams'to diverge outwardly from the tube axis. The potential of electrode 56 is raised until the beams are completely cut oil by the electrode wall portion 64 and no portion of the beam passes through the aperture. This also eifect ively prevents the negative ions in the beams 53 from striking the fluorescent screen of the tube. The current in the magnetic focusing coil 62 is then increased until the beams converge to clear the apertured wall portion 64. Theconvergence of the beams is continued until they are brought to a common point on the screen, after which the beams may be used in any manner desired. Because of the magnetic convergence of the beams by coil 62, the negative ions in the beams are little affected and continue to be trapped by the apertured wall portion 64 of accelerating electrode 56.

Fig. 4 discloses an alternative form of the gun structure shown in Fig. 2. The accelerating electrodes 54 and 56 in Fig. 2 are combined into a common accelerating electrode 65 having an apertured wall portion 66 at the end closest to the fluorescent screen of the tube. Accelerating electrode 65 is tied by spring fingers B8 to the conductive wall portion l0, which extends to a point adjacent to the fluorescent screen. The electron beams, in the manner described for Fig. 2, enter accelerating electrode 65 substantially along parallel paths symmetrically arranged about the tube axis. trode wall 66 is smaller than that in the ion blocking wall $4 of Fig. 2. In combining electrodes 5d and 55 of Fig. 2 into a single electrode 65, the divergent action of electrodes 54 and 56 on the electron beams is eliminated. In order I that the electrode structure 66 of Fig. 4 effectively trap the negative ions the electrode wall 66 must effectively block the parallel beam paths entering the electrode 65. The magnetic coil 12 is used to converge the electron beams so that they pass through the central aperture in plate 66 while the negative ions of the beam continue on and strike wall 56.

While certain specific embodiments have been illustrated and described, it will be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. An electron discharge device comprising electrode gun means for providing a plurality of electron beams along respective paths, said electron gun means including an accelerating electrode having an electron impermeable portion thereof positioned in the path of each elec- The aperture in the electi tron beam and an aperture therethrough, means for producing a magnetic focusing field for directing said beams from their respective beam paths through the aperture of said accelerating electrode.

2. An electron discharge device comprising a plurality of electron guns symmetrically arranged about an axis for providing a plurality of electron beams along respective paths, an accelerating electrode common to said electron guns having an electron impermeable portion thereof positioned in the path of each electron beam, said accelerating electrode having an aperture therethrough surrounding said axis, and a magnetic field producing means for directin said beams from their respective beam paths through said accelerating electrode aperture.

3. An electron discharge device comprising electron gun means including a plurality of apertured electrodes coaxially spaced along a common axis and a plurality of cathode electrodes symmetrically spaced about said axis for providing a plurality of electron beams along respective paths, said electron gun means including an accelerating electrode having an electron impermeable portion thereof positioned in the path of each electron beam, said accelerating electrode having an aperture therethrough surrounding said axis, and a magnetic field producing means for directing said beams from their respective beam paths through said accelerating electrode aperture.

4.. An electron discharge device comprising a plurality of electron guns arranged parallel to each other and symmetrically spaced about an axis for providing a plurality of electron beams along parallel paths, an accelerating electrode common to said electron guns having an electron impermeable portion thereof positioned in the path of each electron beam, said accelerating electrode having an aperture therethrough surrounding said axis, and a magnetic field producing means for directing said beams from their respective beam paths through said accelerating electrode aperture.

5. An electron discharge device comprising a plurality of electrodes and an electron source symmetrically arranged about an axis for providing a plurality of electron beams along respective paths, a pair of accelerating electrodes spaced along and surrounding said beam paths from said electrodes, lead means connected to said accelerating electrodes for applying different potentials to said accelerating electrodes to form an electrostatic field therebetween for changing the direction of said electron beams along divergent paths, said accelerating electrode positioned farther from said electrodes having an electron impermeable portion thereof positioned in the divergent path of each electron beam, said accelerating electrode having an aperture therethrough surrounding said axis, and a magnetic field producing means for directing said beams from their respective beam paths through said accelerating electrode aperture.

6. An electron gun structure for providing a plurality of electron beams along respective paths, said structure comprising. a plurality of electron emitting cathode portions directed toward a common axis, an accelerating electrode having an aperture therethrough surrounding said axis, and a control grid electrode portion positioned between each of said cathode portions and said accelerating electrode, said control grid portions each having an aperture theretnroughaisaidiaccelerating;eeleetrodei having; an electron-impermeable portion thQIEQfiIP S Ti IQ inthe pathziefieacnelectron; bee-mm 7 n'An :electren; gun; ,St ll1 Gt11I-r @0134 providinga plurality of electron beams along respective p hsinsaiidn un me e msr zn ira i 1 y of aizkmsie-eleatrodesee ach; hayin en e e tron! emitngisuitfaeepositi ned: M58 a e facing a coinommies; mfllfinartllbulfliliii fi 1916ctrqde .spacegl frcn said cathpde;-electrodescoxiallsew thrsaidwt dnmonrzaxi na d a c mm ont olzgnid e ectredeas a ed between said cathdeve e ro eswand sa d-ac el ra i r d saiq gontrol grid electrode having; an apertured pqrt ion ov erlying each of said electron emitting cathode su itaces and-between said emitting surfaces and said common-axis,-said-accelerating electrode hai ing .an electron: impermeable portion.thereofi pqsitioned' in thelpath of-each elect on beama.

8. Aireleetron gun,- structure,-comprising; electrongungneans ion providing a plurality of electronl beams alongwaralleL-paths and2 symmetaz ly n seoabout an,.=axis, anaccelerating electrode. having an aperture. surrounding said axis and an. electron impermeable .portion thereoi positioned; in the path of each electron beam.

9. electron. discharge (device comprising, eleetron gun rneans including. a source of-electrons ior prpyiding a plurality. ofelectron beams alongyparallel paths... a -..common accelerating eiectroderharinganzapfirtune theretnrcugh ism: roundingisaidbeamzuatkrs, said acceleretingzeleca trode includin an. electron impermeablewall portion, means :fQr dinect/ing; said electron.- beams toward jsaidaimpermeable f -.Wa1l portion,v and .ia magnetic coil surrounding saidubeamvpathsvfon Drcviding;.-a iconverging, magnetic fieldnredi-recting said electron beams throu hpsaidiaccelerate ing. i electrode aperture.

10-. -A 5 cathode. ray; tube;-co1nprising,; electron gun means-iorproiiidinera iilurality of.electron. beams along paths symmetrically disposed 1, about a commonaaxis saidrelectron gun means include ing, an accelerating electrode surroundingifiaid beam paths, gsaid. accelerating =electrode having. an :electron. I impermeable portion thereot positioned in the path of! each electron beam-and an aperture- ;therethrough; on saidaaxis, -means4o1t producing-a :maeneticfocusinghianddeflecting field tor directing said. beams from their said; I85. spective beam, paths through, .the aperture. of said accelerating. electrode.

DAWD DALENAN OBMERQ:

References Cited -in-v the file of this patent-:-

UNITED 1 STATES PATENTS Number Name, Date 2,348,133 Iams May 2, 19414 -7175 Parker ,Dec.'28', 1948 2,565,533' Szegho Aug. 2371951 

